Many rotary electrical machines are equipped with a claw rotor. A machine of this type is described hereinafter in the form of a compact polyphase alternator, in particular for a motor vehicle. This alternator transforms mechanical energy into electrical energy, and can be reversible. A reversible alternator of this type is known as an alternator-starter, and in an another operating mode it transforms electrical energy into mechanical energy, in particular in order to start the thermal engine of the vehicle.
This machine substantially comprises a housing, and, inside the latter, a claw rotor which is integral in rotation with a shaft, and a stator which surrounds the rotor, with the presence of a slight air gap, and comprises a body in the form of a set of plates provided with notches equipped with notch insulators for fitting of the phases of the stator, each comprising at least one winding which forms a chignon on both sides of the stator body.
The windings are obtained for example from a continuous wire which is covered with enamel, or from conductive elements in the form of a bar, such as pins which are connected to one another for example by welding. These windings are for example three-phase windings which are connected in the form of a star or a triangle, the outputs of which are connected to at least one rectifier bridge comprising rectifier elements such as diodes or transistors of the MOSFET type, particularly when an alternator-starter is involved as described for example in document FR A2745445.
The claw rotor comprises two axially juxtaposed magnet wheels with an annular form, each of which has a transverse flange provided on its outer periphery, with teeth with a trapezoidal form facing axially towards the flange of the other magnet wheel, with the teeth of one magnet wheel penetrating into the space which exists between two adjacent teeth of the other magnet wheel, such that the teeth of the magnet wheels are imbricated.
The flanges of the wheels have an annular form, and have on their outer periphery radial projections which are connected by chamfers comprising teeth. These projections form claws together with the teeth. The number of teeth depends on the applications, and in particular on the number of phases of the stator.
A cylindrical core is interposed axially between the flanges of the wheels. This core supports an excitation winding on its outer periphery. An insulator, such as a winding support coil, is interposed radially between the core and the winding. The rotor shaft supports on its front end a drive unit, such as a pulley, belonging to a device for transmission of movement to at least one belt between the alternator and the thermal engine of the motor vehicle, and on its rear end with a reduced diameter it supports collector rings which are connected by wired connections to the ends of the excitation winding of the rotor.
Brushes belong to a brush-holder, and are arranged such as to rub on the collector rings. The brush-holder is connected to a voltage regulator. When the excitation winding is supplied electrically by the brushes, the rotor, which is made of ferromagnetic material, is magnetised, and becomes an inductor rotor with the formation of magnetic poles at the teeth of the magnet wheels.
This inductor rotor creates an induced alternating current in the induced stator, when the shaft is rotating, with the rectifier bridge(s) making it possible to transform the induced alternating current into a direct current, in particular in order to supply the loads and consumers of the on-board network of the motor vehicle, as well as to recharge the battery of the said vehicle.
The performance levels, i.e. the power and the output of the rotary electrical machine, can be increased further by using a certain number of permanent magnets, for example twelve or sixteen magnets, arranged symmetrically relative to the axis of the rotor, and interposed between two adjacent teeth on the inner periphery of the stator.
The permanent magnets can be inserted in the magnet wheels by crimping or forging. Crimping has the disadvantage of being a lengthy operation which prolongs the assembly of the shaft on the rotor. In fact, the crimping cycle time is substantial, and it can constitute a bottleneck in the production line. Insertion by forging for its part speeds up the assembly operations, but requires accurate centring of the shaft.
It is known in the prior art to use a shaft comprising grooves for an axial stop and straight knurling for a stop with rotation as described in document FR2905806. This type of shaft has the disadvantage of not ensuring centring of the magnet wheels relative to the shaft which is compatible with magnet wheels with forged magnets.
It is known in the prior art to use shafts comprising a centring area, but with no knurling for the purpose of retention in rotation of the magnet wheels, and no support or collar. These systems have the disadvantage of not guaranteeing satisfactory axial retention of the magnet wheels.
None of the present systems makes it possible to fulfil simultaneously all the requirements, i.e. of permitting the use of magnet wheels with forged slots, which requires accurate centring, and axial retention of the magnet wheels, combined with a reinforced clamping application which permits radial retention of the magnet wheels.